"Maternal dietary exposure to whole wheat during pregnancy may reduce offspring's breast cancer risk by improving DNA damage repair mechanisms," wrote lead author Bin Yu in the International Journal of Cancer (Vol. 119, pp. 2279-2286).
Over one million women worldwide are diagnosed with breast cancer every year, with about 400,000 new cases in Europe. According to the European School of Oncology, the highest incidence rates are found in the Netherlands and the US. China has the lowest incidence and mortality rate of the disease.
The new study, by researchers at Georgetown University, adds to previous studies that have reported a potential relationship between dietary fibre and breast cancer, an effect linked to a reduction in oestrogen levels that are said to promote tumour growth.
Yu and co-workers looked at the effect of supplementing the standard AIN 93 diet of pregnant female rats with six per cent fibre from oat, whole wheat, defatted flax flour, or cellulose (control group). When the babies were born, the mothers were switched back to the standard AIN93 diet.
When the pups reached 50 days of age the researchers gave an injection of a breast cancer-causing agent (5 mg of 7,12-dimethylbenz[a]anthracene - DMBA) to stimulate breast cancer growth.
The Georgetown researchers report that the daughters of rats fed the whole-wheat fibre diet were less likely to develop breast cancer, while the defatted flax flour group were found to be more likely to develop the cancer. Oat flour consumption during pregnancy was not associated with an effect on breast cancer development in the offspring.
A mechanistic study at the onset of puberty (three weeks of age) and five weeks later when the daughter rats were said to be more susceptible to tumour formation revealed that gene expression and mammary gland morphology were changed in the wheat flour offspring.
in utero dietary exposures, appeared to show that the number of so-called terminal end buds (TEBs), the main sites of cancerous transformation, was less in the mammary glands of whole wheat and oat flour offspring, compared to the cellulose control offspring.
The researchers also report that the whole wheat flour offspring had significantly increased mRNA and/or protein levels linked to the genes, BRCA1 and p53, in their mammary glands.
BRCA1 is a so-called breast cancer susceptibility gene. The gene produces a protein, also called BRCA1, which is responsible for repairing damaged DNA in cells. Cells with defective copies of the disease are unable to repair the gene, risking mutation and tumour formation.
Also, the p53 gene is one of a family of genes called tumour suppressors, which code for proteins that prevent damaged cells from reproducing.
Additionally, levels of a marker for DNA damage were significantly reduced in the whole-wheat offspring (8-hydroxy-2 -deoxyguanosine: 8-OHdG). This result, said the researchers, suggested: "that maternal dietary exposure to whole wheat during pregnancy may reduce offspring's breast cancer risk by improving DNA damage repair mechanisms."
Dr. Leena Hilakivi-Clarke, the lead researcher on the study, told Reuters Health: "It might be beneficial to include whole wheat in the diet when one is expecting.
"The model we're using should be relatively valid to make assumptions about what's going on in humans," she said.
Significant further research is needed however before any potential relationship between human fibre intake from whole wheat or other sources may have an effect on the breast cancer risk of female offspring.
Whole grains, a rich source of phytochemicals, bran, fibre, minerals and vitamins, have been gaining increasing attention from researchers, with studies reporting reduced risks of metabolic syndrome, diabetes, and colorectal cancer.
However, the link between colorectal cancer and whole grains has been put down to the fibre content, although this remains an area of intense debate.